that some one know why the दिखाना end like that? why donna and eric not get marrid? and why dose the दिखाना not have "happy end" ?

First off, what are आप talking about? The दिखाना DID have a happy ending! Sure, they all went their separate ways but that's life. Life doesn't always have the perfect ending. If they would have all stayed together it wouldn't be realistic.

Next, Donna and Eric may not have ended up getting married, but they're BACK TOGETHER! Isn't that enough. The दिखाना leaves it up to the audience's imagination to decide what happened after the दिखाना ended, which is just as cool as if they would have actually filmed it.